1. Field of the Invention
The present invention relates passive solar and electric lighting systems.
2. Description of Related Art
Various roof lighting, or skylighting, systems have been developed for directing sunlight through the roof to the building interior.
U.S. Pat. No. 6,604,329, describes a common skylighting system, for those situations where sunlight is to be conveyed through an attic or other extensive ceiling structures. Typically, the light is conducted through an elongated tube, generally square or rectangular in cross-section, and having light reflecting inner surfaces. The tube will extend through the ceiling structures of a building with an upper end covered by a light transmitting skylight attached to the roof of the building and a lower open end covered by a light transmitting and diffusing panel or lens at the ceiling level.
The problem with many such skylighting systems is the highly variable amount of light that is directed into the building interior, due to the variance in the intensity of ambient sunlight from season to season, day to day, and even hour to hour. Further, depending on the climate and season, the intensity of sunlight entering through the skylighting system may be, at times, too much, either in terms of the brightness of the light, or in the heating of the building interior.
Various systems have been proposed to compensate for this variance in light. U.S. Pat. No. 6,827,445, and U.S. Pat. No. 5,493,824, each describe a system for tracking the direction of the sun, to maximize the amount of sunlight entering the skylight opening on the roof. In United States Patent Application No. 2002/0073635, reflective mirrors are incorporated into the systems that change angles to direct reflected sunlight into the building.
Other systems seek to limit the intensity of light entering the system. United States Patent Application No. 2005/0005542, and U.S. Pat. No. 6,000,170, control intensity of sunlight by adding shutters or louvers to the system to reduce the amount of sunlight that enters the building. U.S. Pat. No. 7,222,461, teaches the use of shading surfaces on the roof of the building, to prevent direct sunlight from even passing into roof skylight.
In U.S. Pat. No. 5,729,387, prism plates and light detectors are utilized to precisely control the intensity and direction of sunlight directed through the system.
No skylight system can completely compensate for the variance in sunlight over the course of a day, from dawn to dusk. In some systems, sunlight from the skylighting system is supplemented by artificial lighting in an attempt to even out the variance in light brought into the building. U.S. Pat. No. 6,142,645, teaches one such skylighting system that includes a lighting fixture attached to a lighting opening provided in the frame. This provides an alternative lighting system that can be turned on when the sunlight falls between a certain level.
United States Patent Application No. 2002/0060283, incorporates a light metering device and adjacent artificial lighting light source in the tube, such that when the detected sunlight rate is too low, the artificial light is increase. The problem with this system is that the artificial lighting apparatus shades or blocks the sunlight from entering the building.
The problem remains, then, to provide a lighting system that can seamlessly and efficiently control the intensity of light directed into interior of a building from a skylighting apparatus. None of the prior approaches has been able to provide a simple skylighting system that is adapted to convey a steady source of light year round to a building interior.